Lock bolt placing apparatus

ABSTRACT

The invention relates to a hydraulically operated lock bolt placing tool of the type comprising a double-acting master piston and cylinder and a double-acting slave piston and cylinder, connected together by two conduits to form a hydraulic intensifier. The relative size of the pistons is such that, on the return stroke, an excess of hydraulic fluid is generated in the return conduit. Connected to the return conduit is a hydraulic reservoir with a pressurized inlet valve. This ensures that, on the return stroke of the tool, pressure builds up in the return conduit to provide a force to pull the anvil off the swaged lock bolt collar. The hydraulic reservoir contains resilient sponge rubber.

United States Patent Sanders et al.

[ Mar. 7, 1972 [54] LOCK BOLT PLACING APPARATUS gland [73] Assignee: Aerpat A.G.

[22] Filed: Sept. 29, 1969 211 Appl. No.: 861,960

[52] U.S. Cl. ..6l/54.5 HA, 60/545 H, 60/52, 60/54.6 R, 227/10 [51] Int. Cl ..Fl5b 7/00, B25c 1/12, FlSb 15/18 [58] Field of Search ..60/54.5 H, 54.5 P, 54.5, 54.5 HA; 29/252; 72/391 [56] References Cited UNITED STATES PATENTS 3,039,270 6/1962 Simmons ..60/54.5 HA 2,526,956 10/1950 Kugler ....60/54.5 H

3,442,292 5/1969 Jacuzzi ..92/92 FOREIGN PATENTS OR APPLICATIONS 1,318,026 l/1962 France ..l37/489 Primary Examiner-Edgar W. Geoghegan Assistant Examiner-A. M. Zupcie Attorney-Kemon, Palmer & Estabrook [57] ABSTRACT The invention relates to a hydraulically operated lock bolt placing tool of the type comprising a double-acting master piston and cylinder and a double-acting slave piston and cylinder, connected together by two conduits to form a hydraulic intensifier. The relative size of the pistons is such that, on the return stroke, an excess of hydraulic fluid is generated in the return conduit. Connected to the return conduit is a hydraulic reservoir with a pressurized inlet valve. This ensures that, on the return stroke of the tool, pressure builds up in the return conduit to provide a force to pull the anvil off the swaged lock bolt collar. The hydraulic reservoir contains resilient sponge rubber.

2,551,274 5/1951 MacDuff ..60/54.5 3,254,522 6/1966 Elliottet a1. ..72/391 8C1aims,l0lDrawingFigures PATENTEDMAR 7 I972 SHEET 1 OF 6 Attorneys PATENTEUMAR 7:972 3,646,757

SHEET 2 OF 6 A tlarneys PATENTEDMAR 7 I972 SHEET 4 BF 6 .ESEJP I A ltorneys PAIENTEBMAR 7 i972 SHEET 6 OF 6 mm Q Q R m k wwmm LOCK BOLT PLACING APPARATUS This invention relates to lock bolt placing apparatus.

By lock bolt is meant a fastener of the type comprising a pin with a head at one end and one or more locking grooves on the stem of the pin at a position spaced from the head, and a collar which fits over the stern of the pin and which, in placing of the fastener, is swaged into the aforesaid locking groove or grooves to lock it to the pin.

Such lock bolts are usually placed or set by means of a placing tool which comprises gripping means (e.g., a pair ofjaws) which grip a portion of the stem extending beyond the locking groove(s) of the pin, and an annular anvil which abuts the collar. The pin is inserted through aligned apertures in workpieces to be joined together with the head adjacent one face of the workpieces, and the collar is placed over locking grooves on the part of the pin stem projecting from the other side of the workpieces so that the collar is adjacent the other face of the latter. The placing tool is then offered up to the projecting part of the pin stem so that the gripping portion of the stem goes through the aperture in the annular anvil and is gripped by the gripping means, while the anvil receives and rests against the collar. The tool is then operated (e.g., by hydraulic power) to retract the gripping means with respect to the anvil. The head of the pin is pulled hard against one face of the workpieces and the collar is pushed hard against the other face by the anvil. This push on the anvil increases until the collar deforms and the anvil passes over the collar and swages the collar into the locking groove(s) on the pin stem, thus placing the fastener.

Such lock bolts and lock bolt placing apparatus are well known and are well understood by those skilled in the art of industrial fasteners, one example of such being those commercially available under the Registered Trademark Avdelok."

Considerable force on the anvil is required to deform and swage the collar, and difficulty is sometimes experienced in pulling the anvil off the swaged collar.

The present invention provides lock bolt placing apparatus which comprises:

a hydraulic master piston reciprocable in a master cylinder;

a hydraulic slave piston reciprocable in a slave cylinder;

the slave piston being connectable to stem-gripping means for gripping the stem of a lock bolt, and the slave cylinder being connectable to an anvil for abutting the collar of the lock bolt;

21 first hydraulic connection between one side of the master cylinder and one side of the slave cylinder, such that when the master piston is moved, movement of the slave piston is controlled in accordance therewith by flow of hydraulic fluid along the said first hydraulic connection, and such that movement of the master piston in one direction causes flow of hydraulic fluid along the said first connection from the said one side of the master cylinder to the said one side of the slave cylinder and controls the slave piston to move in a direction to retract the gripping means with respect to the anvil;

a second hydraulic connection between the other side of the master cylinder and the other side of the slave cylinder;

and a hydraulic reservoir connected to the said second hydraulic connection;

the relative dimensions of the master and slave pistons being such that the volumes swept, during such movement of the master and slave pistons, by those faces of the master and slave pistons respectively which are in communication with the second hydraulic connection, are different, such that when the master piston is moved in the said one direction (whereby when the tool is in use the anvil is caused to swage the locking collar on to the stem) there is a deficiency of fluid in the second hydraulic connection which is made up from the reservoir, and when the master piston is moved in the opposite direction there is an excess of hydraulic fluid in the second hydraulic connection which is discharged into the reservoir; the reservoir having a pressurized inlet valve, whereby when the master piston is moved in the said opposite direction hydraulic pressure in the slave cylinder on that side of the slave piston communicating with the second hydraulic connection increases to assist in pulling the anvil off the swaged collar.

The stem-gripping means and the anvil are preferably detachable from the remainder of the apparatus to enable lock bolts of different sizes to be placed by the use of appropriate stem-gripping means and anvils.

Preferably the hydraulic reservoir contains resilient material which contracts to accommodate hydraulic fluid when the latter is discharged into the reservoir and which expands to replace hydraulic fluid when the latter is drawn from the reser- VOII'.

In a preferred embodiment of the invention, the resilient material comprises a body formed with a multiplicity of noninterconnecting voids, e.g., cellular rubber.

In a preferred embodiment of the invention, the hydraulic reservoir comprises a tubular pressure body, and the resilient material is tubular in shape and is a close fit within the bore of the tubular pressure body.

Preferably the pressurized inlet valve is accommodated within the reservoir, preferably within the bore of the tubular resilient material.

Preferably the maximum extent of movement of the master piston is limited to a predetermined distance, and

the hydraulic reservoir is capable of accommodating the whole of the volume of hydraulic fluid displaced by the master piston during movement in the aforesaid opposite direction in the event that the salve piston is prevented from moving by jamming or some other cause.

A specific embodiment of the invention, in the form of a hydropneumatie hand-held lock bolt placing gun, will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a theoretical diagram of the hydraulic circuit of the gun;

FIG. 2 is a vertical axial longitudinal section through the gun (which does not have an anvil and grippingjaws attached to it) on the line IIII of FIG. 3;

FIG. 3 is a section on the lines III-III in FIGS. 2 and 4;

FIG. 4 is an elevation (with part in section) taken in the direction of the arrow IV of FIG. 2;

FIG. 5 is a section (on an enlarged scale) on the line V-V of FIG. 4;

FIG. 6 is a section on the line VIVI of FIG. 5;

FIG. 7 is a partial elevation taken in the direction of the arrow VII ofFIG. 2;

FIGS. 8, 9, and 10 are sections, corresponding to the uppermost part of FIG. 2, showing the gun with an anvil and grippingjaws in use during the placing of a lock bolt, illustrating successive stages during the placing of the lock bolt.

The lock bolt placing gun of this example is conventional in its general arrangement and basic manner of functioning. It comprises a hydraulic master piston 11 working within a master cylinder 12 formed by a cylindrical bore within a main casting 13. The gun also has a hydraulic slave or head piston 14 working within a slave cylinder formed by a transverse bore 15 at the head or top of the main casting. The slave piston I4 can be connected to stem-gripping means by means of an externally threaded portion 16 at one end thereof, and the slave cylinder is connectable to an anvil by means of an externally threaded portion 17 of an adapter 18 which is secured to the head casting around one end of the cylinder 15 (see FIGS. 8, 9 and 10). The threaded portions 16 and 17 are coaxial, and lie at the forward end of the piston 14 and cylinder 15, i.e., that end which in use of the gun is nearer the workpiece. There is a first hydraulic connection, in the form of a short bore I9, between the upper end of the master cylinder 12 (above the master piston 11) and the forward end of the slave cylinder 15 (forward of the slave piston 14). There is a second hydraulic connection 21 between the rearward end of the slave cylinder 15 (behind the slave piston 14) and the bottom end of the master cylinder I2 (below the master piston 11). This second hydraulic connection 21 comprises a main bore 22 within the main casting and running parallel to the master cylinder 12, a short transverse bore 23 connecting the lower end of the bore 22 with the lower end of the master cylinder 12, and a short inclined bore 24 connecting the upper end of the bore 22 with the rear end of the slave cylinder 15.

Connected to the second hydraulic connection 21 is a hydraulic reservoir 25, which is cylindrical in configuration. An inclined oblique bore 26 leads from the lowermost end of the bore 22 to the outside of the outlet valve 27 of the reservoir. Another bore 28, opening out of the bore 26, runs parallel to the reservoir 25 and connects, via a further cross bore 29, with the outside of the inlet valve 31 of the reservoir. (It should be noted that in the theoretical hydraulic circuit diagram of FIG. 1, the bore 26 is shown as meeting the bore 28 at the end thereof nearer the inlet valve 31, whereas in the gun of this example the physical arrangement of the hydraulic bores is as just described above.) As illustrated in FIG. 3, the reservoir 25 comprises the cylindrical bore 33 within a casting 34 forming part of the lower portion of the gun. The bore 33 is blind at one end and has the other end closed by a plug 35. Closely fitting within the bore 33 is a tubular body of neoprene sponge rubber 36. This sponge rubber is of a closed cellular construction, i.e., the rubber is formed with a multiplicity of small cells (in this example, of means diameter of the order of -25 thousandths of an inch) throughout its body, the cells being nonintercommunicating. The body of rubber is highly compressible and resilient. The inside of the tubular body 36 fits closely (when in its undeformed state) around a perforated tube 37, one end of which is located on the body 38 of the inlet valve 31 and the other end of which is received within the plug 35 at the other end of the reservoir. The inlet valve 31 comprises a small spherical steel ball 39 held against its seat by means of a stem 41 under the urging of a strong helical compression spring 42, the stem 41 and spring 42 being accommodated within the perforated tube 37 inside the reservoir. In this example, the inlet valve 31 is arranged so that it does not open until a pressure differential of about 1,500 lbs. per sq. inch exists across it. The outlet valve 27 is also a nonreturn valve, but is arranged to open under a relatively low pressure differential. As illustrated in FIG. 3, the outlet valve 27 is accommodated within the plug 35 sealing one end of the bore 33.

Movement of the master piston 11 within the master cylinder 12 is achieved by a pneumatic piston and cylinder arrangement integral with the gun. The construction and operation of this pneumatic arrangement is well known in hydropneumatic lock bolt placing tools, and will be described only briefly in the present specification. The hydraulic master piston 11 is formed as the upper end of a piston rod 43, the lower end of which protrudes through the bottom end of the cylinder 12 and has secured to it a pneumatic piston 44 working within a pneumatic cylinder 45 which forms the bottom part of the gun. The top of the pneumatic cylinder 45 is closed by the casting 34 referred to earlier. On top of this casting there is arranged, on one side of the bottom of the cylinder 12, the hydraulic reservoir 25, and on the other side a pneumatic valve 46, which is illustrated in detail in FIG. 5. Compressed air is supplied by means ofa compressed air line to an inlet 47. The valve 46 has a valve member 48 which is biassed by means of the helical compression spring 49 into the position shown in FIG. 5. In this position, compressed air from the inlet 47 is fed by means of a hole 51 communicating with one end of the valve chamber and through the casting 34 directly into the upper part of the pneumatic cylinder 45 above the pneumatic piston 44, while the lower part of the pneumatic cylinder 45 below the pneumatic piston 44 is vented to atmosphere by means of a conduit 52 (illustrated in FIG. 4), cross bore 50 communicating with the other end of the valve chamber, and past the valve spring 49. Thus the piston is normally in its lowermost position (not as illustrated in FIG 2). A trigger 53 is connected by means of a mechanical linkage 54 to the valve member 48 of the valve 46. When the trigger 53 is compressed, the valve member 48 is moved to interchange the pneumatic connections. Compressed air is then fed to the bottom of pneumatic cylinder 45, while the top of the pneumatic cylinder is vented to atmosphere. The pneumatic piston 44 has a relatively large area, so that the thrust on the piston rod 43 moves the hydraulic master piston 11 upwards in the cylinder 12. Hydraulic fluid is forced out of the upper part of the cylinder 12, through the bore 19 and into the forward part of the slave cylinder 15, thus driving the piston 14 backwards. The uppermost position of the pistons 11 and 44 is illustrated in FIG. 2. When the trigger 53 is released, the valve 46 returns to its original position and the piston rod 43 is driven downwards, thus returning the hydraulic slave piston 14 forwardly. Since the hydraulic fluid is substantially incompressible, and the gun is primed with fluid so that the whole of the space in front of the slave piston 14, above the master piston 11 and in the connection 19, is full of hydraulic fluid, movement of the salve piston 14 is controlled by movement of the master piston 11 by hydraulic fluid flowing in one direction or the other through the bore 19.

When the master and slave pistons move, there is also a flow of hydraulic fluid along the second connection 21. It will be observed from FIG. 2 that the effective area of the top of the master piston 11 is greater than the effective area of its bottom, and that likewise the effective area of the front of the slave piston 14 is greater than the effective area of its rear. In the gun of this example, these areas are as follows:

Area of Master piston top 0.442 sq. in. Area of master piston bottom 0.245 sq. in. Area of slave piston front L460 sq. in. Area of slave piston rear 0.777 sq. in.

The relationship between these areas is such that, whenever the master piston 11 is moving upwardly and the slave piston 14 is moving rearwardly, the underneath face of the master piston 11 sweeps out a greater volume than the rear face of the slave piston 14. Consequently there is a deficiency of hydraulic fluid in the connection 21, which is made up from the reservoir 25. Similarly, whenever the master piston 11 is moving downwardly and the slave piston 14 is moving forwardly, there is an excess of hydraulic fluid in the connection 21, which is discharged into the reservoir 25. Since the inlet valve 31 of the reservoir cannot open to admit hydraulic fluid to the reservoir until a pressure differential of l,500 lbs. per sq. inch exists across it, pressure in the second hydraulic connection 21 builds up when the master piston 11 is moving downwardly and the slave piston 14 is moving forwardly.

FIGS. 8, 9 and 10 illustrate how the gun is used in placing a lock bolt. An annular anvil 61 is provided at the forward end of an anvil tube 62 which is secured to the slave cylinder 15 by means ofa collar 63 at the other end of the tube screwed onto the threaded position 17 of the adaptor 18. Inside the tube 62 a stem-gripping mechanism 64 is provided at the forward end of a draw tube 65 screwed onto the threaded portion 16 at the front of the slave piston 14. The stem-gripping mechanism 64 is ofa type well known in lock bolt placing tools, comprising a set of three jaws 66 urged into a tapering collet 67 inside the front end of the tube 65 by means of a backup tube 68 and a helical compression spring 69. The inner faces of the jaws are grooved to engage and grip the grooved stem 71 of a lock bolt 72. F rorn the forward end of the draw tube 65 projects a pushoff sleeve 73 which passes through the annular anvil 61 around the stem of the lock bolt in order to contact the rear face of the lock bolt collar 74. FIG. 8 illustrates the start of a placing cycle. The lock bolt 72 has been inserted through an aperture in sheets 75 to be secured together and the collar 74 placed over the projecting stem. The lock bolt placing gun, with the slave piston and jaw mechanism in its forward position has been applied to the lock bolt, so that the annular anvil 61 is in contact with the rear of the lock bolt collar 74, with the grooved stem 71 ofthe lock bolt engaged between the jaws 66 and firmly gripped by them. This is the position illustrated in FIG. 8. The operator then depresses the gun trigger 53, so

that the slave piston 14 is retracted into the cylinder 15. Since the lock bolt stem is securely gripped within the jaws 66, the anvil 61 is forced over the collar 74, deforming it and swaging it into locking grooves (not seen in the drawings) on the lock bolt stern underneath the collar. This movement continues until the build up of deformed material of the collar prevents the anvil 61 moving further along the deformed lock bolt. Since the pull on the draw tube 65 is still increasing, the lock bolt stern then breaks, under the increasing tension on it, at a breaker groove which is situated between the locking grooves and the jaw-engaging grooves. FIG. 9 illustrates the position when the breaker groove has just broken, one side of the deformed breaker groove beingjust visible at the outside end of the swaged collar, and indicated by the reference numeral 76. The operator will normally release the trigger 53 as soon as the bolt stem breaks, although it is usually found that the slave piston 14 has had time to move further rearwardly on the sudden release of resistance to its movement on the breaking of the stem. During the whole of the rearward movement of the slave piston, the deficiency of hydraulic fluid in the connection 21 previously mentioned has been made good from the hydraulic fluid stored within the reservoir 25, fluid being drawn out through the nonreturn outlet valve 27.

When the trigger 53 is released, movement of the master piston 11 is reversed, so that there is a reduction in the hydraulic pressure in front of the slave piston 14 and an increase in hydraulic pressure behind it. As soon as downward movement of the master piston 11 and forward movement of the slave piston 14 starts, there is produced an excess of hydraulic fluid in the connection 21, which can be discharged only into the reservoir through the pressurized inlet valve 31. Consequently the hydraulic pressure in the connection 21 and behind the slave piston 14 immediately builds up to, and remains at sufficient pressure to open the inlet valve 31. As the slave piston 14 moves forwards, so does the jaw mechanism 54 carrying the broken bolt stem with it. The forward end of the broken portion of the bolt stem then contacts the broken rear end of the placed lock bolt. As the draw tube 65 continues to move forwards, the broken portion of the stem pushes the jaws 66 backwards out of their tapered collet 67, although the jaws continue to grip the broken stern since they are firmly engaged in the grooves. Rearward movement of the jaws is limited by a shoulder 77 within the draw tube 65. As the draw tube 65 continues to move forwards with respect to the anvil tube 62, the forward end of the ejector sleeve 73 then contacts the rear of the lock bolt collar which is swaged onto the lock bolt. The considerable pressure differential which still exists across the two sides of the slave piston 14 provides sufficient forward thrust on the ejector sleeve with respect to the anvil to pull the anvil off the swaged collar.

This removal of the anvil from the swaged collar has previously presented difflculties, since a considerable force is necessary to remove the anvil. The pull on the anvil must be directly axially backwards, without any twisting or transverse force on the anvil with respect to the collar, which would tend to distort the anvil. In the gun of the foregoing example, the thrust on the ejector sleeve pulls the anvil 61 off the swaged collar, thus disengaging the gun from the placed lock bolt, and returning the various parts of the gun to their initial position.

During the whole of the forward movement of the slave piston 14, the excess hydraulic fluid in the connection 21 has been accommodated within the hydraulic reservoir 25, by the compression and reduction in volume of the cellular foam rubber cylinder 36. When, on the next placing action of the gun, hydraulic fluid is withdrawn from the reservoir 25, the rubber cylinder 36 expands again to fill up the space occupied by the withdrawal of the fluid, the resilience of the rubber assisting in ejecting the fluid through the nonreturn outlet valve 27.

It is sometimes found that the slave piston may be prevented from returning forwardly, for example due tojamming of the jaws. The reservoir of the gun of the foregoing example is capable of accommodating, in addition to the excess hydraulic fluid normally produced on the return stroke, all ofthc further excess which would not bc accommodated due to the nonreturn of the slave piston during the full return (i.e., downwards) stroke of the master piston. This is a considerable advantage from the safety point of view, since the high pressures which could otherwise be produced have been known to burst open a lock bolt placing gun. The capability of the reservoir to absorb this extra excess fluid is due to the resilient filling provided by the sponge rubber cylinder.

The hydraulic lock bolt placing gun of this example is also advantageous in the way mentioned above, namely that it provides automatic pushoff of the anvil from the swaged lock bolt collar. Furthermore the particular arrangement of the various parts of the gun in this example, with the pneumatic valve 46 and hydraulic reservoir 25 positioned on the top of the pneumatic cylinder 45, provides a neat and compact gun. The gun is provided with a synthetic plastics cover 77 (illustrated in chain lines in FIGS. 2 and 7), the upper part of which provides a convenient handgrip, and the lower part of which encloses the pneumatic valve and the reservoir and is perforated to allow the passage of air. The accommodation of the pres surized inlet valve 31 within the hydraulic reservoir, and particularly within the tubular rubber body 36, also leads to compactness of construction.

The invention is not restricted to the details of the foregoing example. For instance, instead of the single straight anvil tube and draw tube illustrated in FIGS. 8, 9 and 10, an offset nosepiece may be used.

The lock bolt placing tool may be supplied to a user substantially in the form illustrated in FIGS. 1 to 7, i.e., without the anvil, jaws and associated mechanism, for use with such mechanism which the user already has. Alternatively, the tool may be supplied complete with such mechanism.

We claim:

1. Lock bolt placing apparatus incorporating a closed hydraulic circuit and comprising:

a double-acting hydraulic master piston reciprocable in a master cylinder;

a double-acting hydraulic slave piston reciprocable in a slave cylinder;

the slave piston being connectable to stem-gripping means for gripping the stern of a lock bolt, and the slave cylinder being connectable to an anvil for abutting the collar of the lock bolt;

a first hydraulic connection between one side of the master cylinder and one side of the slave cylinder, and a second hydraulic connection between the other side of the master cylinder and the other side of the slave cylinder, said first and second hydraulic connections remaining uncorrected with each other throughout their operation and such that when the master piston is moved in either direction movement of the slave piston is controlled in accordance therewith by flow of hydraulic fluid along the said first hydraulic connection, and such that movement of the master piston in one direction causes flow of hydraulic fluid along the said first connection from the said one side of the master cylinder to the said one side of the slave cylinder and controls the slave piston to move in a direction to retract the gripping means with respect to the anvil and such that movement of the master piston in the opposite direction over substantially the whole of its stroke causes flow of hydraulic fluid along the said second hydraulic connection from the said other side of the master cylinder to the said other side of the slave cylinder and causes the slave piston to return,

a hydraulic reservoir connected to the said second hydraulic connection by means of pressurized inlet valve means and pressurized outlet valve means;

the relative dimensions of the master and slave pistons being such that the volumes swept, during such movement of the master and slave pistons, by those faces of the master and slave pistons respectively which are in communication with the second hydraulic connection, are different,

such that when the master piston is moved in the said one direction whereby when the tool is in use the anvil is caused to swage the locking collar on to the stem there is a deficiency of fluid in the second hydraulic connection which is made up from the reservoir, and when the master piston is moved in the opposite direction there is an excess of hydraulic fluid in the second hydraulic connection which is discharged into the reservoir;

said pressurized inlet valve means requiring such pressure to open it that when the master piston is moved in the said opposite direction hydraulic pressure in the slave cylinder on that side of the slave piston communicating with the second hydraulic connection increases to assist in pulling the anvil off the swaged collar.

2. Lock bolt placing apparatus as claimed in claim 1, in which the hydraulic reservoir contains resilient material which contracts to accommodate hydraulic fluid when the latter is discharged into the reservoir and which expands to replace hydraulic fluid when the latter is drawn from the reservoir.

3. Lock bolt placing apparatus as claimed in claim 2, in which the resilient material comprises a body formed with a multiplicity of noninterconnecting voids.

4. Lock bolt placing apparatus as claimed in claim 3, in which the resilient material is cellular rubber.

5. Lock bolt placing apparatus as claimed in claim 2, in which the hydraulic reservoir comprises a tubular pressure body, and the resilient material is tubular in shape and is a close tit within the bore of the tubular pressure body.

6. Lock bolt placing apparatus as claimed in claim 1, in which the pressurized inlet valve is accommodated within the reservoir.

7. Lock bolt placing apparatus as claimed in claim 5, in which the pressurized inlet valve is accommodated within the bore of the tubular resilient material.

8. Lock bolt placing apparatus as claimed in claim I, in which the maximum extent of movement of the master piston is limited to a predetermined distance, and in which the hydraulic reservoir is capable of accommodating the whole of the volume of hydraulic fluid displaced by the master piston during movement in the aforesaid opposite direction in the event that the slave piston is prevented from moving by jamming or some other cause. 

1. Lock bolt placing apparatus incorporating a closed hydraulic circuit and comprising: a double-acting hydraulic master piston reciprocable in a master cylinder; a double-acting hydraulic slave piston reciprocable in a slave cylinder; the slave piston being connectable to stem-gripping means for gripping the stem of a lock bolt, and the slave cylinder being connectable to an anvil for abutting the collar of the lock bolt; a first hydraulic connection between one side of the master cylinder and one side of the slave cylinder, and a second hydraulic connection between the other side of the master cylinder and the other side of the slave cylinder, said first and second hydraulic connections remaining uncorrected with each other throughout their operation and such that when the master piston is moved in either direction movement of the slave piston is controlled in accordance therewith by flow of hydraulic fluid along the said first hydraulic connection, and such that movement of the master piston in one direction causes flow of hydraulic fluid along the said first connection from the said one side of the master cylinder to the said one side of the slave cylinder and controls the slave piston to move in a direction to retract the gripping means with respect to the anvil and such that movement of the master piston in the opposite direction over substantially the whole of its stroke causes flow of hydraulic fluid along the said second hydraulic connection from the said other side of the master cylinder to the said other side of the slave cylinder and causes the slave piston to return, a hydraulic reservoir connected to the said second hydraulic connection by means of pressurized inlet valve means and pressurized outlet valve means; the relative dimensions of the master and slave pistons being such that the volumes swept, during such movement of the master and slave pistons, by those faces of the master and slave pistons respectively which are in communication with the second hydraulic connection, are different, such that when the master piston is moved in the said one direction whereby when the tool is in use the anvil is caused to swage the locking collar on to the stem there is a deficiency of fluid in the second hydraulic connection which is made up from the reservoir, and when the master piston is moved in the opposite direction there is an excess of hydraulic fluid in the second hydraulic connection which is discharged into the reservoir; said pressurized inlet valve means requiring such pressure to open it that when the master piston is moved in the said opposite direction hydraulic pressure in the slave cylinder on that side of the slave piston communicating with the second hydraulic connection increases to assist in pulling the anvil off the swaged collar.
 2. Lock bolt placing apparatus as claimed in claim 1, in which the hydraulic reservoir contains resilient material which contracts to accommodate hydraulic fluid when the latter is discharged into the reservoir and which expands to replace hydraulic fluid when the latter is drawn from the reservoir.
 3. Lock bolt placing apparatus as claimed in claim 2, in which the resilient material comprises a body formed with a multiplicity of noninterconnecting voids.
 4. Lock bolt placing apparatus as claimed in claim 3, in which the resilient material is cellular rubber.
 5. Lock bolt placing apparatus as claimed in claim 2, in which the hydraulic reservoir comprises a tubular pressure body, and the resilient material is tubular in shape and is a close fit within the bore of the tubular pressure body.
 6. Lock bolt placing apparatus as claimed in claim 1, in which the pressurized inlet valve is accommodated within the reservoir.
 7. Lock bolt placing apparatus as claimed in claim 5, in which the pressurized inlet valve is accommodated within the bore of the tubular resilient material.
 8. Lock bolt placing apparatus as claimed in claim 1, in which the maximum extent of movement of the master piston is limited to a predetermined distance, and in which the hydraulic reservoir is capable of accommodating the whole of the volume of hydraulic fluid displaced by the master piston during movement in the aforesaid opposite direction in the event that the slave piston is prevented from moving by jamming or some other cause. 